The opera “Aleko” is a graduation work composed by Rachmaninoff, for which the opera was born in Russia in the nineteenth century and has a strong literary and artistic value. This study tries to extract the time-frequency melodic characteristics of the opera “Aleko” by using the spectral analysis technique as a research tool combined with the Fourier transform and constant Q transform. From the perspective of quantitative analysis, the innovative laws of Rachmaninoff’s melodic features are summarized with the intention of revealing the great artistic charm of this opera work. The results of the spectral analysis show that the amplitude of the first part of “Aleko” is 27.5dB, which forms its unique “Rach’s style” through its innovative “stepped” meandering tones. At the same time, the rich melodic layers of “Aleko” emphasize the drama of the opera and make the internal structure of the phrases stronger.